The present invention relates to optical devices, which are controlled by electrochemical processes.
Optical switches, operable by the application of an electric field are known. For example, U.S. Pat. No. 6,542,264, to Agranat, et al., dated Apr. 1, 2003 and entitled, “Electro-holographic optical switch,” whose disclosure is incorporated herein by reference, discloses an optical switch formed of a paraelectric photorefractive material, within which one or several latent holograms are stored, wherein their reconstruction, or activation is controllable by the application of an electric field. The holograms are formed by spatial modulation of the refractive index of the paraelectric photorefractive material, which arises from the quadratic electro-optic effect induced by the combined action of a spatially modulated space charge within the paraelectric photorefractive material and an external applied electric field. U.S. Pat. No. 6,542,264 further discloses a switching network, such as a multistage network, for use in an optical communications system, incorporating at least one optical switch according to the invention.
However, the operation of the optical switches of Agranat et al. requires carefully controlled temperatures, to maintain the material in the paraelectric phase.
Additionally, U.S. Pat. No. 5,684,612, to Wilde, et al., dated Nov. 4, 1997, and entitled, “Method and system for maintaining and controlling the signal-to-noise ratio of holograms recorded in ferroelectric photorefractive materials,” whose disclosure is incorporated herein by reference, describes a hologram with a dynamically controlled diffraction efficiency and enhanced signal-to-noise ratio, which is recorded in ferroelectric photorefractive materials, such as strontium barium niobate (Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6) (SBN), BSTN, SCNN, PBN, BSKNN, BaTiO.sub.3, LiNbO.sub.3, KNbO.sub.3, KTN, PLZT and the tungsten bronze family. The diffraction efficiency of the hologram is dynamically controlled by applying an electric field along the polar axis of the ferroelectric photorefractive recording medium. Electrically controlled diffraction is used in conjunction with hologram fixing and operation of the material at a temperature in the vicinity of or above its Curie temperature to additionally provide prolonged, low-noise readout. The general methods for recording and reconstructing a hologram (or a set of multiplexed holograms), using these techniques is disclosed. A plurality of configurations employing the improved hologram are disclosed, including an optical crossbar switch in guided-wave and free-space formats that can function as a component in a variety of parallel optical processing systems, a reconfigurable dynamic wavelength filter, and a page-based holographic data storage system.
However, the operation of the optical switch of Wilde et al. requires the application of high voltages, in the range of 10 kV.
Transparent materials, whose index of refraction changes with the concentration of a dopant, are known. These include, for example, transition metal oxides, such as V2O5, Ta2O5, MnO2, CoO2, NiO2, Mn2O4, WO3, TiO2, MoO3, IrO7, a combination thereof, as well as a combination of the aforementioned oxides with other oxides, for example, cerium oxide, which may improve the optical properties of the material. Another transparent material, whose index of refraction changes with the concentration of a dopant, is silicon. Rubin et al., [M. Rubin, K. von Rottkay, S.-J. Wen, N. O. zer, and J. Slack, “Optical Indices of Lithiated Electrochromic Oxides,” Solar Energy Materials and Solar Cells, 54 (1998) 49-57, Lawrence Berkeley National Laboratory, University of California, Berkeley, Calif. 94720, USA] provide measured values for a few of these materials.
For example, the data presented by Rubin et al., include complex refractive index of WO3 for wavelengths from 300 to 2500 nm as a function of intercalated charge density of Li ions. FIG. 1, which is based on these data, illustrates the effect of Li ion concentration on the real part of the index of refraction, for a wavelength of 1500 nm. As Li ion concentration increases from 0 to 68 mCcm−2 μm−1, the real part of the index of refraction for a wavelength of 1500 nm increases from about 1.9 to about 2.2. Similar data are presented for other materials, such as V2O5, for which as Li ion concentration increases from 0 to 80 mCcm−2 μm−1, the real part of the index of refraction for wavelengths of between about 900 and 2500 nm increases from about 2.0 to about 2.4. Data are also presented for LixNi1˜xO, LixCoO2, and CeO2—TiO2.
U.S. Pat. No. 5,311,350, to Hiramatsu, et al., dated May 10, 1994, and entitled, “Optical device and apparatus using the optical device,” whose disclosure is incorporated herein by reference, an optical device, comprising a light transmitting optical member of a high molecular material containing mobile ions, and a pair of electrodes formed on surfaces of the optical member, a required potential difference being provided between the electrodes so as to cause ion conduction in the optical member and to reversibly vary a refractive index of the optical member. According to this invention, a refractive index is reversibly varied due to ion conduction, whereby the modulation of a transmitted beam or a reflected beam by the optical device can be reversibly controlled.
The ability to absorb ions makes the transitional metal oxides suitable as electrodes, for high-energy-density batteries. A discussion of this type of electrode may be found in the Handbook of Batteries, second edition, edited by David Linden, and published by McGraw-Hill (1994).
Additionally, U.S. Pat. No. 4,310,609, to Liang, et al., dated Jan. 12, 1982, and entitled, “Metal oxide composite cathode material for high energy density batteries,” whose disclosure is incorporated herein by reference, describes an electrochemical cell, which includes cathode materials, comprising at least one metal oxide, at least one metal, or a mixture of metals or metal oxides incorporated in the matrix of a host metal oxide. The cathode materials are constructed by the chemical addition, reaction, or otherwise intimate contact of various metal oxides and/or metal elements during thermal treatment in mixed states. The materials thereby produced contain metals and oxides of the groups IB, IIB, IIIB, IVB, VB, VIB, VIIB, and VIII, which includes the noble metals and/or their oxide compounds. The incorporation of the metal oxides, metals or mixtures thereof substantially increases the discharge capacity and the overall performance of the cathode materials.
Similarly, U.S. Pat. No. 6,085,015, to Armand, et al., dated Jul. 4, 2000 and entitled, “Lithium insertion electrode materials based on orthosilicate derivatives,” whose disclosure is incorporated herein by reference, describes an orthosilicate whose structure is based on SiO.sub.4.sup.4 tetranions, which contains at least one transition element with at least two valence states. Lithium ingresses or egresses into or from the structure in order to compensate for a change in valency of the redox couple during electrode operation and thereby maintain overall electroneutrality.
Furthermore, U.S. Pat. No. 6,183,910, to Praas, et al., dated Feb. 6, 2001, and entitled “Electrochemical lithium secondary element,” whose disclosure is incorporated herein by reference, describes a material which are suitable as an active cathode, for an electrochemical lithium secondary cell are oxygen-deficient spinels Li.sub.1+x Mn.sub.2-x O.sub.4-.delta, where 0.1toreq.x.1toreq.0.33 and 0.01.1toreq.delta.1toreq.0.5. Their region of existence in a phase diagram laid out between the corner points MnO, MnO.sub.2 and Li.sub.2 MnO.sub.3 for lithium manganese oxide compounds is defined by the corner compounds LiMn.sub.2 O.sub.4, Li.sub.2 Mn.sub.4 O.sub.7, Li.sub.8 Mn.sub.10 O,sub.21 and Li.sub.4/3 Mn.sub.5/3 O.sub.4, all the compounds along the lines LiMn.sub.2 O.sub.4 --Li.sub.4/3 Mn.sub.5/3 O.sub.4 and LiMn.sub.2 O.sub.4--Li.sub.2 Mn.sub.2 O.sub.4 being excepted. The spinels are produced by a modified ceramic process from a mixture of Li-containing and Mn-containing starting substances whose reaction product is reduced by roasting in an Ar/H.sub.2 atmosphere. The Li components x can be replaced partially or completely by foreign monovalent or multivalent cations from the series consisting of Co, Mg, Zn, Ni, Ca, Bi, Ti, V, Rh or Cu.
Transparent materials, whose index of refraction changes with the concentration of a dopant, are used in electrochromatic display devices, which change color when an electric potential is applied. For example, U.S. Pat. 4,060,311, to Green, dated Nov. 29, 1977 and entitled, “Electrochromic device,” whose disclosure is incorporated herein by reference, discloses an electrochromic device, operative as a display device, which changes color on application of an electric potential. The electrochromic device is in the form of a cell comprising a first electrode, a metal-sensitive transition metal oxide in contact with the first electrode and a solid fast ion conductor as the electrolyte in contact with the oxide.
Similarly, U.S. Pat. No. 4,256,379, also to Green, dated Mar. 17, 1981, and entitled, “Electrochromic device,” whose disclosure is incorporated herein by reference, discloses an electrochromic device, operative as a display device, which changes color on application of an electric potential. The electrochromic device is in the form of a cell comprising a metal-sensitive compound having a thickness of 1 micrometer or less, preferable between 0.5 and 0.05 of a micrometer, is described in contact with a solid fast ion conductor as electrolyte. The fast ion conductor itself is in contact with an electrode capable of providing ions the same as the fast ions of the conductor.
It is furthermore known, that materials whose index of refraction changes with the concentration of a dopant may be used as tunable electrochromic filters. For example, U.S. Pat. No. 4,501,472, to Nicholson, dated Feb. 26, 1985, and entitled, “Tunable electrochromic filter,” discloses a device usable as a tunable light filter or as a light valve having an electronically isolated element of a solid, insoluble material capable of reversibly changing state by reaction with soluble reactants. The state-changing element receives the reactants by diffusion through an electrolyte from a generator electrode.
The electrochromatic, or smart windows is a known application that extended from the tunable electrochromic filters. With smart windows users can block either all, or some of the light by simply turning a knob, for example, in order to save on cooling costs.
For example, U.S. Pat. No. 5,699,192, to Van Dine, et al., dated Dec. 16, 1997, and entitled, “Electrochromic structures and methods,” whose disclosure is incorporated herein by reference, relates to monolithic electrochromic devices through which energy, including light, can be transmitted, reflected or absorbed under controlled conditions and describes an electrochromic device, which is applied to a substrate. The electrochromic device includes an electrochromic electrode layer, a counter electrode layer, and an ion-conducting layer sandwiched between those two layers and electrically isolating them from each other, in which the ion-conducting layer is substantially uniform across the substrate and comprises an inorganic superstructure with associated organic material and with a microstructure, which facilitates the transfer of ions. Methods for producing these devices are also disclosed, including depositing the ion-conducting layer on the substrate in the form of a solution, and effecting gelation of that solution.
Furthermore, U.S. Pat. No. 5,708,523, to Kubo, et al., dated Jan. 13, 1998 and entitled “Counterelectrode for smart window and smart window”, whose disclosure is incorporated herein by reference, describes a counterelectrode for a smart window contains a transparent electrically conductive substrate and a plurality of electrically conductive dots arrayed on the transparent electrically conductive substrate. Each of the electrically conductive dots contains fine particles having capacitance of not less than 1 farad/g or fine particles capable of storing electrical charge of not less than 1 coulomb/g. A smart window contains the aforementioned counterelectrode.
Descriptions of smart windows may also be found in C. G. Granquist, “Electrochromism and Smart Windows Design,” Solid State Ionics 53-56, (1992) 479-489, F. E. Ghodsi et al, “Optical and electrochromic properties of sol-gel made CeO2-TiO2 thin films,” Electrochimica Acta 44 (1999) 3127-3136, and C. G. Granqvist, Electrochimica Acta 44 (1999) 3005-3015.
A similar effect may also be obtained without an electrolyte. For example, U.S. Pat. No. 5,202,788, to Weppner, dated Apr. 13, 1993, and entitled, “Electrochromic device with ionically or mixed ionically-electronically conductive electrolyte,” whose disclosure is incorporated herein by reference, describes an electrochromic device which is especially suitable as a window, mirror or display element, characterized by a multi-layer construction with at least one layer, enclosed between two coated electrodes, of a material which is either ionically- or mixed ionically- and electronically-conductive, whereby at least one of the two electrode layers consists of transparent material and the ionically- or ionically- and electronically-conductive material is at least so long transparent as no excitation takes place by the application of voltage via the electrodes.